Extraction of Co(II) from aqueous hydrochloric acid solutions into organic Alamine 336-m-xylene systems was investigated. Extraction experiments were conducted with initial metal concentrations of 1, 3 and 6 g L(-1), each at 1, 5, 8 and 10 M HCl. It was observed that the extractability of Co(II) increases with increasing acidic molarities. Alamine 336 diluted with m-xylene was found to be a suitable extractant for Co(II) for 5 to 10 M. In parallel, extractant volume-domain dynamics were investigated. A mathematical model was developed to correlate metal extractability and Alamine 336 volume content. Optimal Alamine 336 contents were estimated for single stage extraction. (c) 2006 Elsevier B.V. All rights reserved.